Advanced gastrointestinal (GI) solid tumors, in particular adenocarcinoma of the pancreas, remain largely resistant to current standard chemotherapeutic agents. Inducible chemoresistance is attributed to the ability of neoplastic cells to overcome apoptosis, or programmed cell death. Importantly, the activation of the transcription factor NF-r.B has been shown to diminish the genotoxic effects of current anticancer therapies, in a variety of malignancies. NF-rd3 is activated in response to numerous factors (TNFt_, radiation, chemotherapy), and is regulated primarily through a complex interaction with an inhibitor protein, Ird3 [1 I]. In response to these factors, Ird3 is phosphorylated resulting in rapid ubiquitination and proteolysis by the proteasome; phosphorylation of Ird3 involves two key catalytic subunits of Ird3 kinase (IKK), IKKct and IKK_. Ultimately, NF-r,B is involved in the suppression of apoptosis, control of proliferation, suppression of cellular differentiation, and the induction of cell migration. Recently, our laboratory established that inducible activation of NF-rd3 in a human colon cancer cell line diminished the apoptotic response to chemotherapy (CPT-11) and irradiation [12]. Inhibition of NF-r,B using Ir, B expression or a proteasome inhibitor (PS-341) led to enhanced tumoricidal response to chemotherapy [13]; these studies have resulted in ongoing clinical Phase I trials. A more specific inhibitor of NF-r,B, an IKK inhibitor (PS-1145), may lead to improved combinational strategies, and contribute to the further understanding of NF-rd3 signaling in response to chemotherapy. The NF-rd3-regulated genes involved in chemoresistance are poorly characterized, and activation of NF-r,.B in pancreatic cancer is in the earliest stages of investigation. Preliminary data indicate that NF-rd3 is constitutively expressed in pancreatic cancer cell lines, and activated in response to standard chemotherapy (5-fluorouraeil and gemcitabine). Whether NF-r,B inhibition represents a novel target-directed strategy to enhance cytotoxicity of chemotherapy agents in pancreatic cancer remains to be seen. Furthermore, NF-KB may regulate other signaling mechanisms which impact on the efficacy of cancer therapy. NF-rd3 negatively regulates Jun N-terminal kinase (JNK) activation and TNF- induced JNK activity appears to be anti-apoptotic when NF-KB is suppressed. The major goals of this proposal are to characterize the role of NF-r,.B in the chemoresistance of pancreatic cancer, with an emphasis on identifying signaling pathways regulated by NF-r_ to block cancer therapy.
